Press sealed lamps have been used with metal clamp structures to position the lamp for many years. Typically the press seal has a groove, slot, bump or some other formation that is used to align the lamp with respect to the metal support. The metal clamp is then integrated with a lamp base for final electrical connection and mechanical positioning. The coupling of the press seal and clamp requires some thought. Since the two materials are hard, a variance in the manufacture of either component is not easily accommodated. Where the base alignment is improper, the lamp filament may be mispositioned with respect to the expected optical path. Where the components are too tight, or too loose, separation or breakage during assembly or replacement may occur. Examples of press seal lamps with metal bases may be seen in U.S.Pat. No. 3,001,097 and U.S. Pat. No. 3,256,508.
A generally useful method is to form a hard protective base, with an oversized cavity to receive the press seal. The excess cavity volume is then filled with a cement that hardens around the press seal when the lamp is correctly positioned. Unfortunately, cementing and individually aligning each lamp is time consuming, and therefore expensive in terms of mass production. Examples of press seal lamps with cemented bases may be seen in U.S. Pat. No. 4,243,907 and U.S. Pat. No. 4,785,218.
Applicant in a U.S. Pat. No. 4,603,278, 4,752,710 and 4,724,353 described lamp and base structures using a molded lamp base. In essence, applicant described a press seal lamp captured in a molded plastic base. The base in one embodiment has a clipping cavity to receive the press seal. The plastic has sufficient flexibility to open slightly to receive the inserted press seal, but is sufficiently hard to hold the inserted lamp firmly in a nearly fixed position. The lamp leads are extended out through holes in the bottom of the plastic base and folded over the exterior surface of the base where they are captured in formed surface features and held for electrical contact. These molded plastic base lamps have proved to be commercially successful, and are currently made in the millions for use as automobile taillights.
A small percentage of the plastic base lamps fail. The failed lamps generally do not fail immediately after manufacture, but take a period of time to fail. Some of the failed lamps show a crack in the press seal. Since the press seals are not cracked prior to insertion, do not crack during insertion, and are substantially protected from abusive contact once they are positioned in the plastic bases, it is has not been apparent what causes the press seal cracking. Applicant has discovered a cause for the press seal cracks and now teaches a solution to the problem.